Light-emitting diodes have different light-emitting principles and structures from conventional light sources and advantage of small volume and high reliability, hence they can have versatile applications. For example, light-emitting diodes may form a variety of large-scale components on demand to apply to indoor or outdoor displays. Therefore, the brightness enhancement is always an important issue in the manufacture of light-emitting diodes.
FIG. 1A is a schematic diagram of a conventional light-emitting diode. As shown in FIG. 1A, the light-emitting diode includes a substrate 110, a multi-layer epitaxial structure 130 having a light-emitting layer 131 on the substrate 110, and a reflective layer 150 between the multi-layer epitaxial structure 130 and the substrate 110. The reflective layer 150 is configured to reflect the light downward from the light-emitting layer 131 back above the light-emitting layer 131. However, the light beams with larger incident angles, such as light R1 and light R2, would be gradually absorbed by the light-emitting layer 131 after passing back and forth through the light-emitting layer 131 due to the total internal reflection, and consequently the brightness and the luminous efficiency of the light-emitting diode would be reduced. FIG. 1B is a schematic diagram of another conventional light-emitting diode. As shown in FIG. 1B, the light-emitting diode includes a transparent substrate 120 and a multi-layer epitaxial structure 130 having a light-emitting layer 131. When the light from the light-emitting layer 131 is reflected at the bottom of the transparent substrate 120 and travels to the sides of the transparent substrate 120, some light beams (such as light R3) would be reflected back inside the light-emitting diode because its incident angle θ1 is larger than the critical angle θc, and have more chances of being absorbed by the light-emitting layer 131. Therefore the brightness and the luminous efficiency of the light-emitting diode are reduced.
Consequently, it is necessary to provide a light-emitting diode and a method of forming the same capable of reducing the times the light passing through the light-emitting layer.